Axial cam structures are utilized for example in traction roller transmissions in which the traction surfaces are forced into firm engagement with one another with a force which depends on the torque transmitted through the transmission. A planetary type traction roller transmission utilizing axial cam structures is shown for example in applicant's U.S. Pat. No. 4,052,915. An infinitely variable traction roller transmission also utilizing an axial cam structure for forcing the toric discs into engagement with the motion transmitting traction rollers therebetween is disclosed in applicant's U.S. Pat. No. 3,810,398. It is noted that these transmissions should be capable of transmitting torque in either direction. The axial cam structures therefore must be relatively low. In any case, with ball or roller cams axial movement of the two elements provided with the opposite cam surfaces cannot be greater than the ball or roller diameter. A cam structure of the type which is capable of transmitting torque forces in both directions of transmission operation and which includes rollers is shown in detail in applicant's U.S. Pat. No. 4,454,788 where the rollers 22 are disposed between the cam surfaces 20 and 21 of the opposite cam members 17 and 15. While such an arrangement provides for large axial forces it does not provide for large axial travel of the two members separated by the cam structure.
However, for some applications it is important to provide for relatively large axial torque-dependent relative movement and also to provide for such axial movement in a relatively small space.
It is the object of the present invention to provide a cam structure which fulfills the above requirements and which furthermore is inexpensive and easy to manufacture.